The W3C validator is a great tool. It allows developers to quickly and easily find and fix the inevitable problems that creep into any markup document.

As well as the quick’n'easy version, the advanced interface allows you to get a more verbose output. Until recently, one of the options was to view an outline of the document being validated. I found this feature very useful: I could see at a glance whether or not the order of my headings (H1, H2, etc.) made sense.

A little while back, the outline functionality disappeared. This wasn’t deliberate, but it turns out that it was due for deletion anyway. There’s actually a different dedicated service for examining the semantic structure of documents: the semantic data extractor. This tool will do outlining and more. Personally, I think it’s a bit of a shame that validation and outlining have been split into two different services, but both services are immensely useful in their own right.

For a quick and easy way to validate the current document in your browser, drag this bookmarklet to your bookmarks bar and click on it whenever you want to run a check:

If you need to do batch validation, check out this desktop validator, which is available for Mac OS X, Windows, and Linux.

But don’t forget that the W3C validator is there for your benefit. If you think it can be improved in any way, be sure to give your feedback. Consider joining the mailing list, or simply hanging out in the IRC channel, #validator on the freenode network.

The validator I think is a really valuable tool both for users and in helping standards deployment. I’d like it to check (even) more stuff, be (even) more helpful, and prioritize carefully its errors, warning and mild chidings. I’d like it to link to an explanations of why things should be a certain way.

The W3C validator is already a great tool. With the help of developers like you, it can become even greater.